KD fittings often consist of two basic parts, one of which is secured into the edge of one panel and the other of which is fitted into the surface of another panel, and lies substantially flush with the surface. To join the panels at right angles the part projecting from an edge of one panel is secured within the part recessed into the other panel, with the two panels held at right angles.
In one particular type of KD fitting which has been widely used the part that fits into an edge of a panel is a pin made of plastics material, the pin having a shank which is pushed into a hole drilled into the edge of the panel and a head which, when the pin is fully inserted, projects beyond the edge of the panel so as to be engageable with the other part of the fitting. The shank part of the pin is split and has external teeth and a bore runs through the centre of the pin so that after inserting the pin into the hole in the panel a thin steel rod can be driven into the bore in the centre of the pin to spread its shank thus securing the pin in the edge of the panel. In an alternative form the pin is solid and is simply driven into the hole in the panel edge. An example of a fitting of that general kind is shown in British patent specification No. 1,295,470.
The other part of the fitting, recessed into the other panel, contains a specially formed component having a helicoidal camming surface around it and a screwdriver recess at one end. The camming surface engages with a specially formed head on the pin so that when the component is turned the two parts of the fitting are drawn more tightly together, thus tightening the two panels against each other.
That type of fitting has the advantages that one part of the fitting engages loosely in the other part initially thus providing preliminary location while the fitting is being completely tightened, and it can be tightened, using a screwdriver, by applying less than a whole turn to the cammed screw. Howevere, it also has various disadvantages. The plastic pin is of substantial diameter and therefore it has to be rather accurately located near the centre of the panel thickness. Otherwise, one side of the pin may be too close to the surface of the board in which case there is a risk of bursting the board. The teeth on the outside of the pin have a tendency to damage chipboard material in such a way that the pin is not as securely held within the material as is desirable. Fitting a pin of substantial diameter accurately into the edge of a board is an awkward and expensive operation in mass production. The head end of the pin has to be specially formed to co-operate with the cammed screw, and normally in practice is also cranked relative to the pin shank. Both these factors result in it being necessary for the pin to have a predetermined orientation about its axis when fitted into the panel edge. This increases the expense of fitting the pin into the panel edge. There is also a tendency for the cammed screw to loosen during use, especially if subjected to vibration, which loosens the joint between the panels.
Despite these disadvantages fittings of that kind have been quite widely used for ten years or so.
An object of the present invention is to provide a joining device, or KD fitting, in which one or more of the above disadvantages is substantially reduced.